pqc/external/flint-2.4.3/examples/crt.cpp
2014-05-24 23:16:06 +02:00

69 lines
2.0 KiB
C++

/*=============================================================================
This file is part of FLINT.
FLINT is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
FLINT is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with FLINT; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
=============================================================================*/
/******************************************************************************
Copyright (C) 2011 Fredrik Johansson
Copyright (C) 2013 Tom Bachmann (C++ adaptation)
******************************************************************************/
/*
Demo FLINT program for incremental multimodular reduction and
reconstruction using the Chinese Remainder Theorem.
*/
#include <iostream>
#include "fmpzxx.h"
#include "ulong_extras.h"
using namespace flint;
int main(int argc, char* argv[])
{
if (argc != 2)
{
flint_printf("Syntax: crt <integer>\n");
return EXIT_FAILURE;
}
fmpzxx x(argv[1]);
slong bit_bound = bits(x) + 2;
fmpzxx y(0);
fmpzxx prod(1);
mp_limb_t prime = 0;
for (unsigned i = 0; bits(prod) < bit_bound; i++)
{
prime = n_nextprime(prime, 0);
ulong res = (x % prime).to<ulong>();
y = y.CRT(prod, res, prime, true);
std::cout << "residue mod " << prime << " = " << res;
std::cout << "; reconstruction = " << y << '\n';
prod *= prime;
}
return 0;
}